This invention relates to interconnection technology and more specifically to interconnecting micro-electronic machined mechanical systems (MEMS).
New photonic devices are in development that use micromechanical elements. In principal, micromechanical elements can be built on a variety of platforms. However, the substrate of choice is typically a semiconductor wafer, e.g. silicon. Highly and often elegantly engineered silicon processing can be used to make new device structures that combine the mechanical and optical properties of silicon. An advanced technology, silicon optical bench technology, has been developed to implement this approach. Typically the micromechanical devices or subassemblies are formed in large integrated arrays, referred to here as MEMS, to perform a common function in a parallel mode. The substrate for the arrays is usually a silicon wafer or a large silicon chip. In most instances the MEMS device arrays comprise photonic devices, and are accessed with optical I/O signals.
Among the most promising of the photonic MEMS devices are optical cross connect devices. These may be used in optical networking for routing optical signals from one array of optical channels to another. Optical cross connects are typically made in the form of compact arrays of micromechanical mirrors. An input array, usually a linear array, of optical waveguides are arranged to address the mirror array, which steers optical beams from the input array to a corresponding output array of optical waveguides. The input and output optical channels may be optical waveguides in an optical integrated circuit, or may be arrays of optical fibers.
These optical cross connect devices can switch one of a large number of optical inputs between a selected one of a large number of optical outputs. For example, a 10 fiber input array used with a 10 fiber output array has the capacity to make 100 individual connections. Each channel typically has tens or, in future systems, hundreds of channels wavelength division multiplexed (WDM) together. The information handling capacity of such a switch is extremely large.
State of the art optical networking systems require large compact arrays of micromechanical mirrors. The micromechanical mirrors are electrically operated using control electrodes, and mirror tilt is controlled by electrostatic fields selectively applied to the control electrodes.
In a standard optical networking system, for n input fibers an n2 mirror array is used. Each input fiber accesses an associated row of, for example, ten mirrors and each of the ten mirrors addresses one of ten output fibers. In a typical operating cross connect, for example, the first three mirrors are not activated, i.e. do not intersect the beam path, and the fourth is electrically tilted to intersect the beam path and steer the beam to its associated fiber. In this way the first fiber can address a selected one of ten mirrors and thus a selected one of ten fibers. This n2 mirror array requires two tilt positions, on and off. An alternative mirror arrangement uses 2n mirrors for the same 10xc3x9710 switch. It operates by steering the optical beam to one of ten positions, and has two way tilt capability.
For illustration of the interconnection problem, the n2 embodiment will be analyzed.
A 32 channel WDM system requires a 32xc3x9732 mirror array. With four independent electrical address means per mirror the total number of interconnections is 4096. Moreover, each mirror in the array has an associated IC driver, which may include an amplifier and digital-to analog- converter (DAC). The amplifiers and DACS may each comprise several or many, e.g. six, IC chips. Using conventional circuit board assembly this level of interconnection requires many large printed circuit boards.
We have developed an interconnection system for MEMS device arrays that integrates, on a common system interconnection substrate, the MEM device array with the IC control circuits required to drive the MEM device array. Taking as an example, a MEMS optical switching assembly for a 32 channel WDM switch, and two multiple-chip IC modules per channel, the interconnection system of the invention integrates a 1024 mirror array with 64 modular IC drivers for the mirror array. The IC modules are multichip modules (MCMs) and are socket mounted on the common interconnection substrate using both sides of the substrate. This allows pairs of MCMs serving a given WDM channel to be located in close proximity above and below the common interconnection substrate. A redundant interconnection strategy provides uninterrupted operation and the socket mounting strategy allows rapid replacement of defective parts. A contact pin array may be used for interconnecting the MEM device assembly and the MCMs in the sockets. The use of a contact pin array allows the MEMS devices and the MCMs to be easily demountable for replacement or repair.